Spreewerk also used serial numbers with suffix letters and applied to same serial numbering system as Mauser. Spreewerk production started in 1942 and the secret code was cyq. The third manufacturer of P38 pistols was the Spreewerk factory. In total 323.000 P.38 pistols were produced by Mauser during the Nazi regime. The combination serial number + suffix + production year is unique for every Mauser pistol.The Mauser acceptance stamp is E/135 (until midd 1944) and E/WaA135 (late 1944-45). After reaching serial number10,000z in late 1944, Mauser started again with serial number 1, without a letter suffix. In contrast to Walther, Mauser did not start over with serial numbers at the beginning of every year. The suffix letter increased each time the plant started at serial number 1 again. After the first 10,000 pistols were completed, the firm added a suffix letter to ensure that each pistol had a unique serial number. Mauser started over at serial number 1 each time the number 10,000 was reached. Mauser employed a comparable serial numbering system to the one used by Walther. The secret code for Mauser is byf and is stamped on the slide just above the production year (last two digits). In 1942 the Mauser factory started the production of P38 pistols to fulfill the huge demand for these pistols by the German army. So every month started with a higher suffix letter. The goal of every P38 manufacturer was to produce 10.000 P38 pistols every month. From this combination it is easy to determine the production date of the pistol. The combination of year + serial number + suffix (or no suffix for the first 10,000 pistols) is unique for every pistol. For example: The 25,000th pistol produced in a certain year had serial number 5000b,and the 35,000th pistol produced had serial number 5000c.

The first 10,000 pistols produced at the start of the year had no suffix letter. At the beginning of a new year, both the serial numbers and suffix letters again started over. The letter went up one character each time the serial number once more started at 1. To ensure that every pistol had a unique serial number, the Germans added a suffix letter. The firm started over at 1 when the number 10,000 was reached. Walther used serial numbers ranging from 1 to 10,000. Most of the serial numbers also have a suffix letter. There are periods were ac + production year were stamped next to eachother and periods where this combination was stacked. In addition to the secret code the last two digits of the year of production were also stamped on the slide. This new code was ac and was introduced in august 1940. The secret code 480 for the Walther factory was already abandoned after two months use and replaced by a new code.

Decoding walther p1 serial numbers